I will examine the effects of prenatal exposure to the anesthetic halothane on synthesis of the particulate brain subcellular membranes during development. Pregnant rats will be placed into enclosed cages for up to several hours each day and halothane will be delivered in a stream of air. Halothane will be regulated at levels by simulating environmental conditions experienced by anesthesiologists. Relative synthesis of brain subcellular membranes by experimental rat pups will be compared with synthesis by controls at appropriate ages, for example 20 days in the study of myelin synthesis. A double isotope experiment will be used to compare the metabolic states of experimental and control rats. These will be injected with the 14C and 3H isotopes, respectively, of leucine, for example, in the case of proteins synthesis. Following the incorporation of the radioactive compounds one experimental rat will be paired with a control, their brains removed and combined, homogenized as one sample, and subcellular fractions prepared by ultracentrifugation on discontinuous sucrose gradients. Depending on amounts of radioactivity injected, each double brain homogenate will have a characteristic 3H/14C (dpm) ratio. Any fraction whose synthesis has been altered as a result of the experimental perturbation will have a different 3H/14C (dpm) ratio, which will reflect the change in synthesis by the experimental animal. Isotope effects are controlled for by occasionally reversing the isotope order. In pilot experiments, in which 90 ppm of halothane was administered to the mother and protein synthesis was examined at 23 days in the offspring, I have evidence of a substantial reduction in myelin synthesis. Having observed such an effect in pilot data, other age points will be examined, as well as other levels of exposure.